Range-Doppler (RD) algorithms are widely used in inverse synthetic aperture radar (ISAR) imaging. In the standard RD algorithm, envelope alignment and autofocus are first applied to transform the original data into equivalent turntable target data, and then FFT is used for the image formation. Usually, the migration through resolution cells (MTRCs) due to target rotation is ignored. With the improvement of resolution or the increase of target size, MTRCs cannot be ignored and must be mitigated. For high speed moving targets, the most widely used 'stop-and-go' data model is violated. In this case, the mitigation of MTRCs becomes even more complicated. In the paper, technical issues associated with high resolution ISAR imaging of high speed moving targets are addressed. A preprocessing algorithm is first proposed to convert the non-coherent raw ISAR data into coherent data, then a keystone formatting algorithm developed for the imaging of slow ground moving targets in SAR is applied to mitigate the MTRCs owing to rotational motion, and, finally, a high resolution time-frequency analysis based range-instantaneous Doppler (RID) algorithm is used to produce the focused ISAR image. Numerical examples are provided to illustrate the performance of the proposed approach.

To detect buried landmines, Planning Systems Incorporated (PSI) has developed a Ground Penetrat-ing Synthetic Aperture Radar (GPSAR) system. GPSAR can be used to generate three-dimensional images of mines. It has been shown that the SAR processing in the PSI GPSAR system can greatly improve the image quality and hence the mine (especially plastic mine) detection performance. Since the electromagnetic wave propagation velocity in the soil depends on many factors, inchlding the soil texture, bulk density, as well as water content, and it changes from one location to another, velocity uncertainty is inevitable. It is well-known that for the conventional airborne/spaceborne SAR processing, velocity uncertainty may result in phase errors that will severely blur the SAR image. However, we have observed from experimental examples that the PSI GPSAR system is very robust against the velocity uncertainty. More specifically, under mild conditions velocity uncertainty does not defoeus the image but only scales the image along the depth dimension, and hence will not affcct the mine detection performance. Theoretical analysis is provided to explain this observation. Although our discussion is based on the PSI GPSAR system, it applies to other GPR based landmine detection systems as well.

With conventional pulse-echo ranging approaches it is diffcult to obtain un accurate range measurement needed by a proximity ultrasonic sensor system owing to the limited bandwidth of the transducer. A continuous-wave multifreouencv ranging method is presented to accurately measure the proximity distance for an ultrasonic distance sensor system A novel time delay estimator is derived based on a nonlinear least-squares-fitting criterion for the case where the received signal amplitude is non-negative owing to the acoustically hard reflection To minimise the highly oscillatory cost function an effcient two-stage estimation algorithm is proposed Numerical results show that the estimation algorithm can approach the Cram6r-Rao bound as the signal-to-noise ratio increases.

High range resolution (HRR) moving target indicator radar is becoming increasingly important for many military and civilian applications involving the detection and classification of moving targets within a clutter background. For ground-based HRR radar, when targets are moving slowly or near-broadside and the coherent processing interval or dwell time is not too long, the effects of range migration and range feature distortion can be ignored. Based on this assumption, relaxation-based algorithms that are robust and computationally simple are proposed for HRR feature extraction of moving targets consisting of scatterers closely spaced in range in the resence of stationary clutter. Numerical examples show that the proposed algorithms exhibit super-resolution and excellent estimation performance.

A computationally efficient algorithm, referred to as DS-WRELAX, is proposed for the delay and Doppler scale estimation of multiple moving targets. DS-WRELAX can approach the corresponding Cramer-Rao bounds and exhibits much better convergence properties than existing algorithms.